RKObjectMapping和RKEntityMapping之间的关系 [英] Relationship between RKObjectMapping and RKEntityMapping

问题描述

说我有 JSON ：

{
    "hits": 4056,
    "books": [
        {
            "name": "Book 1"
        },
        {
            "name": "Book 2"
        },
        {
            "name": "Book 3"
        }
    ]
}

我想将此响应映射到 BooksResponse object： p>

I would like to map this response to BooksResponse object:

@interface BooksResponse
@property (nonatomic, assign) NSInteger hits;
@property (nonatomic, strong) NSArray* books;
@end

其中books属性是 CoreData 预订对象。我使用 RKObjectEntity 映射 BooksResponse ，如下所示：

Where books property is an array of CoreData Book objects. I'm using RKObjectEntity to map BooksResponse like this:

RKObjectMapping* booksResponseMapping = [RKObjectMapping mappingForClass:[BooksResponse class]];
[booksResponseMapping addAttributeMappingsFromDictionary:@{
        @"hits" : @"hits"
}];

[booksResponseMapping addPropertyMapping:[RKRelationshipMapping
        relationshipMappingFromKeyPath:@"books"
                             toKeyPath:@"books"
                           withMapping:[self booksMapping]]];

并且booksMapping实现如下：

And booksMapping is implemented like this:

RKEntityMapping* bookMapping = [RKEntityMapping mappingForEntityForName:@"Book"
                                                       inManagedObjectStore:[self managedObjectStore]];
[bookMapping addAttributeMappingsFromDictionary:@{
        @"name" : @"name"
}];

但是每当 RestKit 是崩溃：

CoreData: error: Failed to call designated initializer on NSManagedObject class 'Book'

在执行期间检查 ManagedObjectStore 存在于 RKObjectManager 实例。应用程序在 RKMappingOperation：355 上挂起

I checked, during execution ManagedObjectStore exists on RKObjectManager instance. Application hangs in class RKMappingOperation:355 on line

id currentValue = [self.destinationObject valueForKeyPath:keyPath];

有一种方法可以使plain objectiveC对象和 NSManagedObject ，以便 CoreData ？

Is there a way one can make relationship between plain objectiveC object and NSManagedObject so that only part of JSON response is persisted in CoreData?

推荐答案

这是 RKObjectRequestOperation 和 RKManagedObjectRequestOperation 。因为你只有一个响应描述符，它匹配一个对象（不是一个托管对象），RestKit将使用 RKObjectRequestOperation 。当这样做时，映射期间不能使用托管对象库，因此不能创建托管对象。

This is the difference between RKObjectRequestOperation and RKManagedObjectRequestOperation. Because you only have 1 response descriptor and it matches an object (not a managed object), RestKit will use RKObjectRequestOperation. When it does this, the managed object store is not available during the mapping so no managed objects can be created.

解决方法：

而不是使用1响应描述符，使用2.第一个只是创建 BooksResponse 并将 hits 。第二个创建 Book 并映射名称。

Instead of using 1 response descriptor, use 2. The first just creates the BooksResponse and maps the hits. The second creates the Books and maps the name.

操作完成后，您将获得一个映射响应，其字典包含两个键：null和books。 null键保存 BooksResponse 实例，books键保存 Book 实例。您现在可以更新 BooksResponse 实例来填充关系。

Once the operation is complete, you will be provided with a mapping response whose dictionary contains 2 keys: null and "books". The null key holds the BooksResponse instance and the "books" key holds the Book instances. You can now update the BooksResponse instance to populate the relationship.

请注意，映射响应中的键对应于在2个响应描述符上指定的关键路径。

Note, the keys in the mapping response correspond to the key paths specified on the 2 response descriptors.

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